For the battery I would suggest to simply replace the 2 cells, with 2 other, but lighter, cells. Going back to 1 single cell will require a voltage booster, too much of hassle, especially when you aren't an EE.

Take a look here for example: http://www.all-battery.com/li-polyersinglecells.aspxThe lightest option weights only 0.95 grams. But don't shift to often, because the capacity is only 25 mAh Something a little heavier would be a better choice, for example one with a capacity of 160 mAh weights only 4 grams. For comparision when the orinal cells are of the AA format (14500), the capacity is 900 mAh and the weight is 21 grams a cell. So weight savings with the 160 mAh cells would be: 2*21-2*4=34 grams

And get rid of plastic housing, heat shrink tape is a lot lighter

The 300mAh LiOn batteries weigh the same than the 160mAh ones...so you can reduce the weight 34gr with a 1/3 capacity battery. If the standard battery can survive 1000km, the 300mAh can be a very good option as a race-only battery (much better for cyclocross or TT)

A friend of mine works for Shimano, he is part of their technical support group.Last night, we were talking about modifying the Di2 group - and well, apparently people have been getting about 3,000 miles on them between charges.

Shimano's battery estimate is very conservative. I would be ok with a 1-2 week battery life.

I would think about 500miles or 800km taking into account battery deterioration over time would be more than suffice for 99.9% of the people out there. So, probably 35-40% of the current amperage capacity would be suffice.

Would be most interesting to trim a battery to that weight though.

So... who's willing to sacrifice a battery and a harness here ... that's over EURO$200 to be thrown out the window for an 'experiment' ...

Erm, not to go too Off Topic (and I'll bring it back to the Di2 issue) - but electricity is NOT an energy source. It is a type of energy.At this time, where does the majority of your electricity come from?Petroleum powered (or built) plants. Although it will be better to have a world where vehicular transportation does not emit toxic fumes and harm out environment, we will still have a issue with power. Solar and Wind power are the only possible, minimally petroleum-using-in-process, systems of energy gain. However, even those have issues (we can take this discussion into PM if you want. Or just watch the film "Collapse" as a break down of the concept)

Anyway, back on topic - as I talked with the friend of mine who is a Shimano tech rep, we both agreed that the next true step for electronic drivetrains would to have a system that powers the drivetrain's shifting mechanisms without the need for a large battery. Technology needs to be developed to efficiently utilize the energy we (humans) are expending while on the bike in the first place. You don't shift that often, hence you really don't need that much energy put towards the drivetrain constantly. ... that is what needs to be developed.

Anyway, back on topic - as I talked with the friend of mine who is a Shimano tech rep, we both agreed that the next true step for electronic drivetrains would to have a system that powers the drivetrain's shifting mechanisms without the need for a large battery. Technology needs to be developed to efficiently utilize the energy we (humans) are expending while on the bike in the first place. You don't shift that often, hence you really don't need that much energy put towards the drivetrain constantly. ... that is what needs to be developed.

Mavic's Mektronic had this. Batteries were used solely to transmit shifting requests to the mech. Shifting power came from the mech itself, via the top jockey wheel.

I've often thought that braking is overthought and under utilised on bikes. Ever look at that crazy European dude 's bike that he built from scratch with SPOON brakes?Kinda nuts concept he had going (belt driven and spoon brakes) then I thought about modifications. A tiny interposable roller that spins on the tyre conecting it to friction block could work, but with more relevance to this thread....the roller could be a tiny strontium (or other rare earth) generator, with the first tiny pull of the brakes activating the generator with increasing drop in resistance (electrically) so it causes an increasingly higher mechanical resistance untill the friction blocks then come into play. Kinda a KERS system but without the extra 80HP. The initial reason why I was thinking about this is that it could be built very compact an could fit within the crown of the fork.

_________________Used to race....got too wrinkly and old Updated: Racing again! Thought this was unlikely! Eventually, I may even have a decent race!Edit: HAD a decent race! 16/08/2014

Most electricity in the US (over 60%) comes from coal. Also, why not have regenerative braking? Have a very small battery and every time you use the the front brake a little wheel is spun by the tire. You could even adjust the wheel such that it engaged a mm before the actual brakes so you could coast to an intersection with the wheel making power and then apply the brakes firmly at the end.

_________________For certain parts stiffer is more important than lighter.

No offence intended but we already have a very efficiant way to transfer human energy to power both the "instructions" and the actual shifting. It's called a cable. Really guys. How complicated do you want to get. Remember K.I.S.S

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